book reviews Editor: W . F. KIEFFER College of Woostsr
Wmrter, Ohio
Chemical Bonding Clarifled through Quantum Mechanics
George C. Pimatel, University of California, Berkeley, and Richard D. Spralley, University of British Columbia, Canada. Holden-Day, Inc., San Francisco, 1969. 344 pp. Figs. and tables. 15.5 X 23.5 em. Hardbound, 88.50; softbound, 84.50. This clearly written, non-mathematical introduction to the role of the electron in structural chemistry, with emphasis on the descript,ion of chemical bonds by means of molecular orbitals, for students of general chemistry who will not necessarily continue in the physical sciences, may be the best of its genre. It will probably appeal particularly strongly t o teachers who feel that "all of chemistry is ezplained in quantum mechanics" (authors' italics), that Bahr's proposals "proved to he incorrect in almost every respect," and that "[tlhere is no convenient electron-dot formulation" for, e.g., 13-. The book's eight chapters are devoted t o qualitative, yet physically wellgrounded, discussions of the hydrogen atom; ionization energies and many-electron atoms; H a f ; MO's for simple mole'cules; bonding in covalent, ionic, electron-deficient,, and electron-excess compounds; bonding in solids and liquids (the best chapter, I thought); and, to cover all bets (albeit grudgingly), the contributions to valence theory of Lewis (shared electron-pairs), Pauling (hybridization), Gillespie (VSEPR Model), and Linnett (the Double Quartet Theory). The book concludes wit,h fourteen pages of useful data on ionization energies of atoms and molecules, bond energies, bond lengths, stretching force constants, and dipole moments. There are, however; no prohlems and scarcely m y references to the literature.
-Reviewed
The book is noteworthy for its overall clarity and its generally skillful use of diagrams; for its use (following Slster) of the virid theorem in the discussion of the formation of chemical bonds; far discussions of recently characterized molecules (among some 150 compounds discussed are, e.g., NF, NOF, and C H d ; for its critique of the ionic model; and for its inclusion of Engel's rules for metallic structures. Same fifteen pages are devoted to a schematic, two-dimensional, "pigeon hole" scheme far taking into account, implicity, the orbital-conservancy rule (and the creation, in molecular orbital theory, of antibonding orbitals), in the prediction of bond orders for simple molecules. The same results can be obtained via the more classical, vvsn't Hoff-Lewis-Linnett routewhich, in addition, yields useful predictions regarding the mutual disposition of electrons in molecules and (therefore) molecular geometry. I n general, the third dimension plays a subordin~terole in Pimentel and Spratley's book: the tetrahedron is viewed as "cumbersome" and the role of the Pauli Principle in Linnett's theory is described as "a subtle ; ~ resultH-although ) l f l in ( quantum jmechanical fact, as Lennard-Jones bas stressed, the Pauli Principle is probably the most important principle t o be learned by chemists interested in molecular geometry, and is not( emphasized Pauli, also) merely another theorem of quantum mechanics. Of course, any book on the chemical bond of only 298 pages is likely to omit topics of interest to a. reviewer. Particularly disappointing t o me in this generally commendable book is the failure of the authors to mention-much less to stress-the absolute indistinguishability of electrons and the related, all-important antisymmetrization requirement on wave-
in this Issue
George C. Pimenkl and Richard D. Spratley, Chemical Bonding Clarified through . . .A489 Quantum Mechanics R . Bruce King, Transition-Metal Orgsnometallic Chemistry: An Introduction
. . .A490
Daniel J . Paslo and Cad R. Johnson, Organic Structure Determination
. . .A490
Julius Gmnt, editor, Hackh's Chemical Dictionary
. . .A491
functions. At no point do they exhibit a wavefunction for a many-electron system. As in most treatments a t this level, the discussion stops a t the early HiickelMulliken stage of merely writing outor drawing-~ set of orbitals. Thus the reader never learns (from this book-and others a t the same level) that the orbitals of a Slater-determinant are not uniquely determined, mathematically. He never learns that an?, wbital set in a Slater-type wavefunction may be replaced by any linearly indepndmt combination of orbitals without altering the wavefunctia (except, perhaps, by a constant factor). Aside from accounts of the authors' own contributions to valence theory and some interesting computer-calculated electron-distributian diwrams, the book contains little information on developments in quantum chemistry since the 1930's. Most regrettably, no mention is made of the gradnal development of a useful bridge between the concepts of classical stmctursl theory and the results of molecular quantum mechanics through the important work initiated by LennardJones and coworkers in the 1940's and pursued currently by Ruedenberg and Edmiston and many others, on localized molecular orbitals. I n general, surprisingly little effort is made to present ideas in historical perspective. Bohr's pioneering work, in which he introduced for the first time into tion of angular momentum, and the Correspondence Principle (which allows one to see why his model "works," for hydrogen, since for that atom E is independent of 1, l anddfor large , l n, an integer)all this (along with the model's defieiencies) is described as a "dismal record." Similarly, no attempt is made to present Linnett's theory as a natural eanfluence of two converging lines of thought: (1) classiesl structwd theory, as interpreted by Lewis, and (2) the development in quantum mechanics, based on the esrly studies of Hyllersas on helium, James and Coolidge on hydrogen, and Slater on the alkali metals, of the method of different spatial orbitals for electrons of differ& spins. Like many discussions of bonding in recent texts, the major thrust of Pimentel and Spratley's treatment is an attempt t o base the quantum mechanical theory of the chemical bond on a n analysis of systems that contain only hydrogen. First the hydrogen atom is discussed. The student is presented with a set of rules (to be memorized?) for classifying electronic states differing in orbital angular momentum. I n fact, such momenta are largely quenched in most molecules. h Lewis, Gillespie, Linnett, and others have shown, to discuss intelligently the electronic interpretation of chemistry, it is not necessary (nor, with the general student, do I believe desirable) to begin with (or even to mention) atomic spectra. Next, the bonding in HI+ and HZ is considered. The discussion is interes6 ing-if one accepts on faith the existence of wavefunctiom giving the average kinetic and potential energies cited. Yet, (Continued a page A490)
Volume
47,Number 7,July 1970
/
A489
book reviews by the very nature of the systems considered, the discussion is of limited scope. As Platt has emphasized, these two systems provide us with no insight into the two most important features of chemical affinity: its saturation and its directional character-for the Exclusion Principle has not entered into the problem. The systems are too simple to exhibit structurally interestingfeatures. Evidently it cannot be over-emphasiaed that the proton is a, very speoid case in chemistry. It is the only kernel with no inner-shell electrons. Though stressed by Werner (not mentioned by Pimentel and Spratley) and Lewis (down-graded by P and S), the importance of kernel(or atomic-) sizes (and shapes) in determining the chemistries of the elements receives no systemrstio treatment in this book. The primitive graphic ffomulas given for SO*, SO, and SO?, e.g., bear little relation to known interatomic distances and provide the reader with no clues as to the reasons for the non-existence of FOa- and N04a-. I was troubled, also, by the statement that Plrtnck introduced the "particulate model" of light (hestrenuously opposed, a t first, this extension of his work by Ein: stein); by the implication that the radiusratio rules fit well the observed crystal structures of the alkali halides (approximately 40% of the alkali halides do not obey the simple,~Goldsehmidtradius-ratio rules); by the failure to mention hydrogen-bonding in gaseous hydrogen fluoride in a discussion of dipole moments and heats of vaporization; by the use of the virial theorem (in a discussion of the ionic model) for a system whose (inexact) wavefunction is not allowed to relax (and, thereby, to alter its shape and, correspondingly, the system's kinetic and potential energies) with a change in inter-ionic distance; and by the consistent plscement of hydrogen, the pebble upon which this book is based, in Group I. It might be argued that hydrogen belongs in Group VII andlor Group IV, or in a. Group by itself (vide supra). But in no way does the chemistry of hydrogen, rtnd its bonding in compounds, correspond closely (or, if closely, uniquely) to that of the elements of Group I. Of d l the elements in the Periodic Table, those in Group I are least like hydrogen, except for the charges on their kernels. The hook is relatively free of typ* graphical errors. Several c u p s are missing in Fig. 3-5, however, and several nodal surfaces are missing in Fig. 4-19. In Fig. 4-20 two of the orbitals are mislabelled. A major difficulty with current introductions to the chemical bond that, by dwelling on the hydrogen atom and the hvdro~en-molecule ion, exclude almost everyihing that was l'earned ahout the bond in chemistry prior to 1926 (and include little that has been learned ahout it in quantum mechanics since 1940), is that, with young students, particularly, one must resort frequently to authority. Even in the better treatments, there is a. high density of "telling." At each critical juncture in Pimentel snd Spratley, e.g.,
A490
/
Journal of Chemical Education
appear such phrases as "We find t h a t . . . " and "Quantum mechanics tells us . . . " Often, also, the word "explain" is used where a more accurate word would he "describe," or "rat,ionaliee." What we have is a New Descriptive Chemistry, only now, instead of having to memorize facts that seem important (to the teacher) hut that cannot, at the moment, he related to other facts, it is quantum mechanical terminology, orbital d i e grams, and other approximations that must be memorized. Within its chosen limits, however, this is a superior book. The authors express the hope that teachers as well as students may profit from reading it. I believe they will. I did.
HENRY A. BENT North Carolina State University Raleigh Transition-Metal Organometallie Chemistry: An Introduction
R. Bruce King, University of Georgia, Athens. Academic Press, Inc., New York, 1969. ix 204 pp. Figs. and tables. 15.5 X 23.5 cm. $11.50.
+
For over a hundred years the subject of organometallic chemistry embraced only the "representative" elements, or rather those of the "representative" elements which were metals. Perhaps that
